In this chapter, the synthesis and characterization of nanoparticles (NPs), especially metal chalcogenide NPs, as well as their use in photovoltaic devices including hybrid organic–inorganic solar cells are explored. Such devices are known as potential candidates for low-cost and efficient solar energy conversion and belong to the so-called third-generation solar cells. The different methods of NP synthesis and their development for application in more efficient solar cell devices such as those involving perovskite NPs are also presented. Despite the fact that incorporation of oxides and metal nanoparticles has also been successfully achieved in this class of photovoltaic devices, we choose to focus here on metal chalcogenide NPs in light of their appealing optical and electronic properties. We describe herein a comprehensive review of the historical background and the combination of such nanoparticles with other inorganic materials (all inorganic) or with polymer matrices (hybrid systems) and their characterization techniques. Recent developments on more efficient photovoltaic devices and later strategies for surface chemistry modification, in situ NP synthesis, and ternary systems are also reviewed. These include structure (e.g., energy-band alignment) and materials (e.g., selection and optimization of middle-layer materials) engineering.